Review of Recent LNG Research at HSL and … Gant.pdfReview of Recent LNG Research at HSL and...

HSL: HSE’s Health and Safety Laboratory HSL: HSE’s Health and Safety Laboratory

Simon Gant

PHMSA Pipeline Safety Research and Development Forum Cleveland, Ohio, 16-17 November 2016

Review of Recent LNG Research at HSL and Possible Future R&D Topics

HSL: HSE’s Health and Safety Laboratory 2

Outline

Introduction to HSL

Recent research on LNG hazards – LNG pool fires

– Review of vapor cloud explosion incidents

– LNG spills

Potential LNG R&D topics


Introduction to HSL

Directorate of UK Health and Safety Executive (HSE)

Multi-disciplinary laboratory

– Fire and process safety

– Computational modeling

– Exposure control

– Toxicology etc.

Approx. 400 staff

550 acre test site

– Fire galleries and burn hall

– Largest impact track in EU

– Anechoic chamber etc.


Outline

Introduction to HSL



– LNG spills



LNG Pool Fires: Background

Phoenix large-scale LNG pool fire experiments conducted by Sandia National Laboratories in 2009

Two tests involved ignited LNG spills on water

– 21 m diameter LNG pool

– 83 m diameter LNG pool

83 m pool - unexpected results

– Fire did not extend across LNG pool surface

– Fire significantly higher than predicted

– Very little smoke

© Sandia National Laboratories http://prod.sandia.gov/techlib/access-control.cgi/2010/108676.pdf

http://prod.sandia.gov/techlib/access-control.cgi/2010/108676.pdf




LNG Pool Fires: Background

Hypothesis (proposed by Shell Research Ltd)

– Strong thermal updraft from large fire

– High speed inwards flow of air/vapor into the base of the fire

– Flames unable to spread outwards from central ignition location


Video analysis

– 2-3 m/s flow into base of fire

– Sufficient to arrest flame spread?

Investigation at HSL funded by Shell Research Ltd

– CFD modeling

– Flame spread experiments





LNG Pool Fires: Modeling

CFD modeling aim

– To predict the speed of air/vapor entrained into the base of the fire in the Phoenix test

CFD models tested

– Ansys-CFX: volumetric heat source

– FDS: combustion model

Horizontal Velocity

Methane Concentration

Conclusion

– Speed of entrained air/vapor flow

Ansys-CFX = 3.7 m/s

FDS = 3.2 m/s

– Phoenix test provides only one data point

– Mid-scale experiments proposed


LNG Pool Fires: Experiments

Main findings

– Flame stabilised when air flows were 2.8 and 3.2 m/s

– Flame progressed further along low speed areas adjacent to walls

– Stabilised conditions equated to turbulent flame speed of 2 m/s

Flames spread upwind on surface of LNG spill

Fan speed adjusted until flame spread is arrested

Air

Ignition

Wind tunnel experiments


LNG Pool Fires: Conclusions

Inwards flow of air/vapor exceeds 2 m/s when pool diameter > 20 m

Implies maximum LNG pool fire diameter on open water is 20 m

– BUT … obstacles, such as the loading boom in Phoenix tests, would allow the fire to spread > 20 m

– Wind speeds > 2 m/s will move the pool fire towards the downwind edge of the spill area

Main finding: it may be overly simplistic to assume whole pool spill area will be on fire

– Thermal radiation may be lower on upwind side and higher on downwind side than is currently predicted






LNG Pool Fires

Further information

– Atkinson G., Betteridge S., Hall J., Hoyes J. and Gant S.E. "Experimental determination of the rate of flame spread across LNG pools", IChemE Hazards 26 Conference, Edinburgh, UK, 24-26 May 2016

– Betteridge, S., Hoyes, J., Gant S.E. and Ivings, M. "Consequence Modelling of Large LNG Pool Fires on Water", IChemE Hazards 24 Conference, Edinburgh, UK, 7-9 May 2014

– Kelsey A., Gant S.E., McNally K., and Betteridge S. "Application of global sensitivity analysis to FDS simulations of large LNG fire plumes", IChemE Hazards 24 Conference, Edinburgh, UK, 7-9 May 2014


Outline

Introduction to HSL



– LNG spills



Aim: to review historical severe unconfined VCE incidents

– Characterise the events and identify common factors

– Improve our understanding of vapor cloud development and explosion

Motivation

– Public concerns about potential for VCEs at LNG export terminals in USA

– Recent VCEs at Buncefield, Jaipur, San Juan and Amuay produced unexplained high over-pressures in unconfined, uncongested areas

Jaipur (2009) Puerto Rico (2009) Buncefield (2005) Amuay (2012)

Review of Vapor Cloud Explosions (VCEs)


Occurrence of VCE incidents

– No unconfined VCE incidents with methane, only with higher hydrocarbons

– Most VCE incidents involved vapor clouds that spread in all directions around source, indicating the events took place in very low wind speeds

– Only a few incidents showed burned area extending solely in the downwind direction

VCE consequences

– Ignition of large flammable vapor clouds produced high over-pressures and extensive damage in nearly all cases, even in open unconfined areas

– Only one flash fire incident: Donnellsen (Iowa) LPG pipeline, probably due to rich vapor concentrations

Review of VCEs: Main findings


Possible explanation for trends in occurrence of VCE incidents

– Nil/low wind speeds occur less frequently than windy conditions…

– … but small leaks are much more likely than catastrophic failures

– Balance of probabilities: more incidents occurred in nil/low wind speeds

– Incident sites also lacked working gas detection/shutoff systems

– Limited ignition sources (a large cloud could develop before igniting)

Implications

– Importance of gas detection/shutoff systems and other layers of protection

– Significance of small sustained releases in nil/low wind speeds

– Proposed basis for risk assessment: ignition of a large cloud with a concentration well within the flammable range will produce a severe explosion

Other issues

– Lack of consensus among experts on explosion mechanism: deflagration/detonation

Review of VCEs: Conclusions


Further information

– Atkinson G., Cowpe E., Halliday J. and Painter D. (2016) “A historical review of vapour cloud explosions”, Mary Kay O’Connor Process Safety Symposium, Texas A&M, College Station, Texas, 25-27 October 2016

– Atkinson G., Hall J. and McGillivray A (2016) “Review of vapor cloud explosion incidents”, Health and Safety Laboratory Report MH/15/80 http://primis.phmsa.dot.gov/meetings/MtgHome.mtg?mtg=111

– Atkinson G. (2016) “Vapor Cloud Explosion (VCE) Historical Review”, PHMSA Public Workshop on Liquefied Natural Gas (LNG) Regulations, Washington D.C., 19 May 2016, http://primis.phmsa.dot.gov/meetings/MtgHome.mtg?mtg=111

– Multimedia packages available from PHMSA for Buncefield, Jaipur, Flixborough and San Juan incidents

Review of VCEs

http://primis.phmsa.dot.gov/meetings/MtgHome.mtg?mtg=111

http://primis.phmsa.dot.gov/meetings/MtgHome.mtg?mtg=111


Outline

Introduction to HSL



– LNG spills



LNG Spills: Aims

Improve understanding of the physics of LNG spills on land

Conduct experiments to provide data for validating:

– Liquid spread models (non-volatile)

– Models of spreading vaporising pools

Validate HSE’s models of spreading vaporising pools (GASP)

1s 2s


LNG Spills: Experiments

Three fluids: water, liquid nitrogen, LNG

Instantaneous and continuous releases

– Instantaneous volumes: 10 – 30 liters

– Aspect ratio of cylinder: 1:1 – 5:1

Wet and dry concrete test pad (10 × 10 m)

33 configurations with up to 3 repeats

Measurements

– Two rakes of 16 thermocouples above surface to measure spreading rate

– 6 thermocouples embedded in the concrete at depths of 10 – 30 mm

– 3 thermocouples within release cylinder

– Video


LNG Spills: Progress

Analyses of experimental data nearing completion

GASP modeling nearing completion

SPLOT liquid spill model sensitivity tests ongoing

Completion date: March 2017


Outline

Introduction to HSL



– LNG spills



Potential LNG R&D Topics

LNG tank design and consequence modeling

– Jet fire impingement tests

LNG Spills

– Sloping bunds, impoundments, gravel pits

– Use of floating insulating blocks to reduce LNG vaporization rate

– Vapor fences and water sprays/curtains for vapor dilution

Vapor Cloud Explosions

– Large-scale tests: • 100m+ radius vapor fence filled with flammable vapor from LPG fountain

• Study effect of elements that might trigger transition to severe explosion (sheds, pipework etc.)

• Also useful for LPG source terms and low wind dispersion - both urgently needed

– Small-scale tests: • Detonation tests on columnar objects (struts, small pipes, etc.)

• Fundamental studies of the fluid mechanics of flow driven by a localized explosion - boundary layer detachment and roll up, lofting of particles etc.


Acknowledgements

The contents of this presentation, including any opinions and/or conclusion expressed or recommendations made, do not necessarily reflect policy or views of HSE.

Work presented here was funded by:

– Health and Safety Executive (HSE)

– US Department of Transportation Pipeline and Hazardous Materials Safety Administration (PHMSA)

– Shell Research Ltd

Sincere thanks to:

– David Painter and Harvey Tucker (HSE)

– Julie Halliday (PHMSA)

– Simon Rose (ORNL)

– Steven Betteridge (Shell Research Ltd)

– Graham Atkinson, James Hoyes, Rachel Batt Jonathan Hall, Matthew Ivings (HSL)

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